Catalytic transformation of benzoic anhydrides into fluorenones and

FLUORENONES AND BIPHENYLS FROM BENZOIC ANHYDRIDE

J. Org. Chern., Vol. 35, No. 10, 1970 3233

Further Observations on the Catalytic Transformation of Benzoic Anhydrides in to Fluorenones and Biphenyls JOCHANAN BLUM,DAVIDMILSTEIN,AND YOELSASSON Department of Organic Chemistry, Hebrew University, Jerusalem, Israel Received March 6, 1970 The catalytic conversion of benzoic anhydrides into fluorenones and biphenyls by several rhodium compounds has been studied. Mixtures of aromatic anhydrides react generally as if they were mixed anhydrides, leading to the formation of asymmetrically substituted products. Equimolar amounts of the isolated phenyl-rhodium complex PhRhCl(PPh8)z (7) and chlorocarbonylbis(tripheny1phosphine)rhodium (2) react at 250’ to give fluorenone and biphenyl. Both these compounds are assumed to be formed via the same rhodium intermediate.

I n a previous publication’ it has been shown that benzoic anhydride and some of its derivatives can be transformed catalytically by chlorotris(tripheny1phosphine)rhodium(I), RhCl(PPh3)g (l), and by chlorocarbonylbis (triphenylphosphine)rhodium(I), RhC1(CO) (PPh3)z (Z), into fluorenones, benzoic acids, carbon monoxide, small quantities of benzophenones, and, according to the experimental conditions, into varying amounts of biphenyls. We have now extended this study, exploring the scope of the reaction and the possibility of using mixt w e s of anhydrides for the synthesis of fluorenones and biphenyls. In addition to 1 and 2, several other rhodium complexes, as well as anhydrous rhodium trichloride, proved to be effective catalysts for these reactions (Table I). Palladium dichloride, hydrated ruTABLE I CONVERSION OF BENZOIC ANHYDRIDE TO FLUORENONE AND BIPHENYL BY VARIOUS CATALYSTS Catalysta

---Reaction--------Yield-Temp, Time, Fluorenone, Biphenyl, OC hr mol % mol %

RhCl(CO)(PPhs)Z’ 35-52 2.2-3 240 4.5 RhCl(PPh3)sb 240 4.5 36-40 6-7 RhCla, anhydrous 290 6.5 26 3.6 Rhz(C0)JX 250 4 22